Processing of semi-conductor wafers into finished electronic components typically requires many processing steps where the wafers must be handled and processed. The wafers are very valuable, and are extremely delicate and easily damaged by physical and electrical shocks. In addition, successful processing requires the utmost in cleanliness, free of particulates and other contaminants. As a result, specialized containers or carriers have been developed for use during processing, handling and transport of wafers. These containers protect the wafers from physical and electrical hazards, and are sealable to protect the wafers from contaminants. It is important that the containers remain sealed when in use to prevent damage to the wafers from contaminants. It is also important from a process efficiency standpoint that carriers be easily useable and cleanable.
Various configurations of door enclosures and latching mechanisms for sealable wafer carriers are known in the art. Some known latching mechanisms use rotary members for actuating the latch, such as a cam. A problem, however, with such mechanisms is that the cam member can self-rotate at undesirable times. This self-rotation can cause unlatching of the door and exposure of the wafers to contaminants. When the door is not in place on the carrier, self-rotation can cause extension of the latches, making it difficult to reinstall the door on the carrier. Other latching mechanisms use systems of interlinked latching arms actuated by a rotary or sliding element. Such systems can have similar problems with actuation of the latching mechanism at undesired times and by intended means.
Previous methods used with cam actuated latching mechanisms for restraining cam rotation have typically involved a simple leaf spring with a bent tip arranged tangential to the cam. As the cam is rotated near the rotational limit of travel where it is to be held, a surface or projection of the cam slides past the bent tip of the leaf spring. The cam is then held in position at a favored position by the spring force of the leaf spring and friction between the parts. Such a mechanism does not generally urge or spring-bias the cam member toward the favored position to prevent further cam rotation should the cam be dislodged from the detent. Moreover, if two favored positions are provided corresponding to the latch-open and latch-closed position, two separate leaf springs are needed to adequately address both conditions. This adds complexity to the mechanism and complicates assembly of the parts. The leaf springs, if formed from plastic material, do not generally have sufficient rigidity in bending to generate enough friction to hold the cam in position. Alternatives, such as metallic materials, are undesirable in that sliding contact between such materials can generate damaging particulates. Other known methods involve simple detent systems, involving for example, projections from the cam member that engage structures on the door. Such simple detents, however, can become disengaged at unintended times and by unintended means. Once a detent is disengaged, the simple detent mechanism provides no biasing force urging the cam member back toward the detent to prevent latching or unlatching of the door.
Accordingly, what is needed is a device or apparatus that provides favored positions for a wafer carrier door latching mechanism, and that also provides some type of biasing force urging the latching mechanism toward the favored positions to resist further movement of the latch in the event it is dislodged from the favored positions.